Until President Donald Trump's lawyers made their claim that he enjoys unfettered presidential authority, the most sweeping such contention had come from the only president ever forced to resign.

"When the president does it, that means that it is not illegal," Richard Nixon told David Frost in an interview in May 1977, nearly three years after he resigned the presidency in the face of likely impeachment and conviction.

David Frost (left) talks with former President Richard Nixon in this March 1977 file photo prior to the taping of his interview with the former president.

(The Associated Press)

But, in fact, Nixon bowed to the federal courts at each stage in the 26-month scandal known as Watergate after contesting efforts by special prosecutors Archibald Cox and Leon Jaworski to force his hand.

When the Supreme Court ruled he had to turn over tape recordings likely to incriminate him, Nixon did so, a decision he signaled months earlier when his attorney, the well-known legal scholar Charles Alan Wright, told a federal court, "This president does not defy the law."

That is the very issue that remains in doubt with Trump: whether he would defy judicial authority if, for example, the Supreme Court ruled he had to obey a subpoena from special counsel Robert Mueller to testify, and whether any such defiance would, as some claim, trigger political consequences such as impeachment.

A non-lawyer, Trump has shown repeated disdain for the federal courts. As a candidate, he inappropriately raised the ethnicity of the judge who was considering a suit against his for-profit colleges and, in his early days as president, he denounced federal judges rejecting his initial presidential dictum limiting immigration from certain predominantly Muslim countries.

In addition, Trump has generally taken an expansive view of his presidential powers, on issues ranging from federal ethics laws to his recent highly political pardons that seemed designed to signal to potential witnesses he would protect them.

His most significant assertions of presidential authority have come in dealing with the Justice Department, ranging from his demands to investigate Hillary Clinton and reveal investigatory information to his repeated denunciation of Attorney General Jeff Sessions' recusal from the Russia inquiry.

According to The New York Times, Trump told advisers during a 2017 anti-Sessions discussion that he expected his top Justice Department official to protect him the way he claimed Robert Kennedy protected President John F. Kennedy and Eric Holder protected President Barack Obama.

"Where's my Roy Cohn?" he reportedly asked, referring to the lawyer and fixer who handled many matters for him during his days as a New York real estate developer.

That raised the question of whether Trump understood that, unlike the White House counsel, the Justice Department represents the American people, not the president.

But the most far-reaching Trump claim came in the secret memo submitted last January by Trump lawyers John Dowd and Jay Sekulow to Mueller, which was published last weekend by The New York Times.

After listing various events it said Mueller's office wished to address in its investigation of possible obstruction of justice and collusion with the Russians, the letter declared, "It remains our position that the president's actions here, by virtue of his position as the chief law enforcement officer, could neither constitutionally nor legally constitute obstruction because that would amount to him obstructing himself, and that he could, if he wished, terminate the inquiry, or even exercise his power to pardon if he so desired."

In other words, Trump has the power to fire anyone involved in the inquiry — potentially directed at him — without potential sanction, because he can't legally or constitutionally obstruct himself.

Most of the initial debate focused on the assertion that Trump can pardon himself.

That's a "really interesting constitutional argument," another Trump attorney, Rudy Giuliani, said on ABC's This Week, seeking to clarify the president's position but perhaps muddying the waters.

Whatever the legalities, the former New York mayor added, the political ramifications would be tough. "It would lead to probably an immediate impeachment," he said on NBC's Meet the Press.

Of course, the focus on the president's pardon power seems premature. The more immediate issue is likely to be whether Mueller can compel Trump to testify, and whether he would obey a court order to do so.

By saying that the president's actions "could neither constitutionally nor legally constitute obstruction," Dowd and Sekulow appear to be laying the basis for challenging any Mueller effort to question Trump about those matters. As Giuliani noted on This Week, Trump's shifting explanation about the Trump Tower meeting with Russians "is the reason you don't let the president testify."

It's hardly surprising that Trump and his lawyers want to signal he will fight any effort to force him to testify in the Russia probe. They seem to be counting on the fact that, even if the courts demand it and he refuses, he'll retain the support of enough spineless congressional Republicans that, unlike Nixon, he can get away with it.

Carl P. Leubsdorf is the former Washington bureau chief of The Dallas Morning News and a frequent contributor. Email:carl.p.leubsdorf@gmail.com